The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Acid fracturing is utilized to etch flowpaths in the fracture face that remain open after the fracture closes, and to penetrate deeply away from the wellbore creating flowpaths (e.g. wormholes) that help bring fluid more quickly to the fracture and the wellbore. However, acid fracturing of formations involves many challenges. When direct acid fluids are utilized, the acid can react quickly near the wellbore and fail to penetrate deeply into the formation to increase productivity. Further, acid fluids can corrode metal parts and other components in the wellbore, causing excessive wear and picking up undesirable metals in the fracturing fluid that can cause precipitates to form. Therefore, treatments often include retarding the acid and/or limiting the volume or pumping time of a treatment.
Retardation mechanisms known in the art include the use of emulsified acids, the use of low concentration acids, gelled acids, and/or the use of liquids that form acids on contact with water allowing acid to form in the wellbore and/or formation. The use of liquids to form acids also has limited benefit, as acid precursors in a liquid phase react very quickly to become acids thereby limiting the delay effect of generating acid in the wellbore. Further, the introduction of water and/or additional fluid volumes (e.g. due to low acid concentrations) introduces or exacerbates scale formation problems. Scale formation problems can also be a significant problem in formations including carbonates, which are common formations for acid fracturing treatments.
Scale formation in fluid-producing wells can reduce productivity of the well or even stop production completely. Scale formation chemistry is generally understood, and conventional scale inhibition treatments are known in the art. However, currently available scale inhibition treatments suffer from several drawbacks. One conventional scale inhibition method consists of injecting a fluid including a scale inhibitor chemical into a formation, and flushing the chemical away from the wellbore with an amount of follow-up flushing fluid, where the chemical may be designed to adsorb to formation particle surfaces. The scale inhibitor chemical may be included in a water-based or oil-based fluid.
One conventional scale treatment involves coating particles with resin, and coating the resin with scale inhibitor to prevent the resin coated particles from sticking together before treatment is completed, while the scale inhibitor coating provides some scale inhibition after the treatment. Unfortunately, currently available scale inhibition treatments suffer from a few drawbacks. For example, currently available scale inhibition treatments do not inhibit scale for long periods of time and therefore require repeated application. In high flow areas of a well, for example in a fracture, the scale inhibitor is removed by producing fluid quickly reducing the effectiveness of the treatment. Also, the available concentration of scale inhibitor declines rapidly after initial treatment, and therefore the scale inhibition procedure must be repeated often or overdesigned with initial concentrations much higher than required to inhibit scale. Accordingly, there is a demand for further improvements in this area of technology.